The subject of the present invention is a device for adjusting the power of a power pack driving a helicopter rotor, more especially allowing assistance with piloting in emergency backup mode in the event of a failure of the main system for adjusting the speed of rotation of the rotor of the helicopter.
The subject of the present invention is also an adjusting method used in the event of a failure of the main adjusting system.
Helicopter turboengines are equipped with an adjusting system which fulfills a plurality of more or less complex functions. The main function of the adjusting system is nevertheless to adjust, in flight, the power delivered by the turboengine so as to maintain the speed of rotation of the rotor of the helicopter at a substantially constant value.
The adjusting systems which are frequently encountered nowadays are electronic adjusting systems fitted with a manual emergency backup device.
During normal operation, adjustment is managed by an electronic computer which receives signals originating from various sensors and controls various actuators so as to automatically adjust the power delivered by the engine. In the event of a failure affecting the electronic adjusting system and causing the computer to be incapable of adjusting the power delivered by the engine, the pilot of the helicopter must, by means of a manual emergency backup device, manually alter the power delivered by the turboengine as a function of the requirements engendered by the maneuvers of the helicopter (setting of pitch, lowering of pitch, landing, etc.). The piloting burden is substantially increased thereby. Specifically, the pilot must at each instant manually adjust the feed rate of the fuel supplying the turboengine. This is especially constraining on a single-engine helicopter, any maneuver of the helicopter requiring a specific manual alteration of the feed rate of the fuel.
It is therefore necessary for the pilot to be correctly trained for this particular situation. However, in order to decrease the risks which may result from inadequate training of the pilot, the manufacturer of the turboengine is apt to guarantee an extremely low failure rate for the main adjusting system, thereby entailing greater complexity and hence an augmentation in the cost of the adjusting system as a whole.
The subject of the present invention is a simple, inexpensive device making it possible to improve the adjusting of the power of the power pack in the event of a failure of the main adjusting system and to ease piloting in emergency backup mode.
The subject of the present invention is also an adjusting device which increases safety in the event of a failure and is relatively cheap to make.
The device for adjusting the power of a power pack driving a helicopter rotor according to the invention comprises a means of dosing the fuel feed rate, an electronic control device comprising a means of acquisition of an input signal corresponding to the speed of rotation of the rotor (NP), a means of processing said input signal comprising a differentiator element and a summator element, as well as a threshold-based comparator receiving the output signal from said processing means. An actuator device receives the output signal from the electronic control device and progressively actuates the means of dosing the fuel feed rate in the direction of an increase in feed rate, of a decrease in feed rate or of an unchanged maintenance of the feed rate.
Such a device is especially simple, easy to install and to use, owing to the fact that it does not use any manual control, thereby eliminating any lever, linkage, bell crank, etc. In the event of a failure of the main adjusting system, the pilot of the helicopter is no longer obliged to regulate the fuel feed rate manually, it being controlled automatically.
The piloting of the helicopter, in the event of a failure of the main adjusting system, is greatly eased with respect to emergency backup piloting with manual alteration of the power. This because the pilot simply has to adopt gentle piloting, without any abrupt maneuver and to take care to comply with the maximum ratings of the engine as well as the limits on the torque and on the speed of the rotor of the helicopter. The pilot need no longer worry about the fuel feed rate which is overseen automatically by the device of the invention. In particular, the pilot need no longer at each instant manually alter the fuel feed rate in order it to adapt it to the power requirements engendered by the maneuvers of the helicopter such as, for example, settings of pitch, lowerings of pitch, landing, etc.
In an advantageous embodiment, the actuator device is an electric device and the electronic control device furthermore includes a means of electrical supply of the actuator device.
A low-pass filter can be provided in order to perform a filtering of the input signal.
The comparator preferably comprises a predetermined high threshold and a predetermined low threshold.
The actuator device is preferably designed so as to act at relatively low speed and advantageously comprises a minimum position stop. In this way, a signal integration effect is automatically obtained. Moreover, the limitation of the speed of variation of the fuel feed rate which results therefrom makes it possible to accelerate the engine without any risk of pumping. Likewise, the minimum position stop makes it possible to decelerate the engine without any risk of shutdown.
The actuator device can for example be a DC motor whose speed of rotation is constant for a specified supply voltage, or else a stepper motor.
The means of dosing the fuel feed rate can comprise an auxiliary doser of fuel cooperating with a main doser, auxiliary doser acting in parallel with the main doser so as to add some feed rate to the feed rate existing at the moment of the failure and acting in series with the main doser so as to remove some feed rate. As a variant, the dosing means may be a single dosing member controlled by a stepper motor with dual input, the one actuated by the main adjusting system and the other actuated by the device of the invention, in the event of a failure of the main adjusting system.
The invention is especially adapted to the case where the power pack is a turboengine.
The invention also relates, in a more general manner, to a method for adjusting the power of a power pack driving a helicopter rotor in the event of a failure of the main adjusting system, in which the increasing or the decreasing of the fuel feed rate to the power pack is controlled automatically with respect to the feed rate at the moment of the failure, as a function of the speed of rotation of the rotor (NP).
The use as single input signal of the speed of rotation of the rotor allows the implementation of the method of the invention by especially simple and inexpensive means.